This invention relates to a method and apparatus for cleaning an inkjet printhead, and more particularly to a cleaning media and a method of cleaning a page-wide-array printhead with the cleaning media.
Inkjet printers eject liquid ink through multiple nozzles to form characters and graphics on a page. Print quality is dependent upon printer resolution and printhead performance. Printing at a 300 dpi ("dots per inch") resolution yields print quality comparable to 300 dpi laserjet printing. To achieve reliable performance, the inkjet printhead and inkjet process are designed to precisely control inkjet output. By controlling the timing, placement and volume of inkjet output droplets, reliable, repeatable character performance and graphic performance is achieved.
A clogged nozzle adversely impacts the placement and volume of inkjet output droplets as the ink droplet may be deflected from its intended destination and less than all ink may escape the nozzle. A seldom used nozzle may get dried ink or contaminants lodged in its orifice. Hot and dry environmental conditions, for example, speed up the drying process and may cause nozzles to clog. Also, contaminants from the external environment or from the printing process may get lodged in a nozzle blocking an orifice. Such clogging may occur despite design efforts to minimize ink drying and maintain a clean printhead environment. Accordingly, there is an ongoing need to provide methods and apparatii for cleaning inkjet printheads.
Conventional inkjet printheads span less than one inch and are scanned across the page. To perform a print operation the printhead is moved in one direction while the page is moved in a perpendicular direction. In effect the printhead scans the page while ejecting ink droplets to form the desired printout. When not in use the printhead moves into a service area where the printhead is cleaned then capped. As the printhead moves into a rest position, it traverses an elastomeric wiper (e.g., nitrile rubber). The wiper wipes ink from the printhead surface. Scrapers are then used in some embodiments to clean off the wipers.
A page-wide-array ("PWA") printhead spans an entire pagewidth (e.g., 8.5 inches) and includes thousands of nozzles. The PWA printhead thus has many more nozzles than the scanning-type printheads discussed above. The PWA printhead is formed on an elongated printbar. The printbar typically is oriented orthogonally to the paper path. During operation, the printbar and PWA printhead are fixed while a page is fed adjacent to the printhead. The PWA printhead prints one or more lines at a time as the page moves relative to the printhead. This compares to the printing of multiple characters at a time as achieved by scanning-type printheads.
Depending on the printout characteristics, certain nozzles on a PWA printhead may be exercised less than other nozzles. For example, a user may print most of the time using one inch margins, and on occasion use less than one inch margins. The nozzles in the one inch margin area, thus get exercised less regularly, and may clog more readily. This characteristic of uneven nozzle exercise is less common for a scanning-type printhead. Scanning printhead nozzles that start out in the margin area subsequently move out of the margin area and get exercised as the printhead scans the pagewidth.
Thus, certain nozzles on a PWA printhead are more prone to clogging than on a scanning-type printhead. In general, the problem of drying ink is more pronounced for a PWA printhead than for a scanning-type printhead. Accordingly, there is a need for an effective cleaning methodology for PWA printheads.
One solution would be to remove the printbar and clean the printhead in a manner similar to the cleaning of scanning-type printheads. However, to maintain reliable, accurate printing, the printbar is fixed and precisely positioned. There are several mechanical attachments that have to be undone to remove the printbar. Thus, the process would be timely and require careful actions. Also, repeated insertion and removal may wear on the components used for precisely fixing the printbar adding play to the printbar. Thus, it is desirable to use a cleaning methodology for cleaning the printhead while in place.